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Old chevy question

I have a jeep with a 1968 327 chevy in it. I lost the harmonic balancer bolt. Was wondering if anyone knows what size the bolt is.Its fine thread, and its larger than 3/8, but a 7/16 is too big. Motor was rebuilt in 1985 and was wondering if the 350 crank with a metric bolt could have been put in instead of the 327 crank by the engine shop.

I thought they were 7/16" fine. However, Ratlover brings up a good point. A lot of early engines (all 283's, some 327's) were drilled but not tapped, as they were just a press-fit. My old man used to race 283's, and said drilling-and-tapping was very easy to do with handtools (bring the hole size up one bit at a time to help keep it centered. Look closely with a flashlight, may need a little degreaser too. If it isn't tapped, now is a good time to do so. I would do it on any HP application, be it racing or offroading.

The easiest would be to just buy a new one from the dealer, or ARP, or even the wreckers for that matter. Hardware store bolts tend to be cheap, low grade stuff and there is no substitute for a proper GM part.

A 1968 327 could have a 350 crank swapped into it because it has the large journal mains and rods already (previous years were smaller). However, a 350 crank has nearly a 1/4" longer stroke, which would require different pistons (ie: 327 and 350 use the same block) so it cannot be swapped 'by accident' at a shop or the parts would not match. Basically, the crank determines if the engine will be a 327 or 350.